Chromosomes and Karyotypes

REVIEW:

Not all chromosomes are in ‘x’ shape. Humans have 46 chromosomes. 

Bacteria: Circular shape chromosome

Centromere is not always in the center of the chromosome.

There are still 46 chromosomes when it’s duplicated, its just the chromatids that are duplicated.

Karyotype: Image of all your chromosomes, from a cell in mitosis stage typically metaphase

Anaphase And Telophase: NOT the phase to do Karyotype

Metaphase: Has two sister chromatids

Homologous pairs:

22 of the pairs are autosomes.

Last two are called sex chromosomes: 23 chromosomes from fathers (x and y), 23 chromosomes from mothers ( x )

CHROMOSOMES AND KARYOTYPES

  • Chromosomes condense during mitosis and become visible.

  • We take a photo of the chromosomes and then cut and paste them until the chromosomes are paired by length and banding.

  • This picture is called a karyotype.

Karyotype

Karyotype

Karyotypes show the number and types of chromosomes in a eukaryotic cell.

The chromosomes are stained and photographed to generate a visual profile

  • The chromosomes of an organism are arranged into homologous pairs according to size (with sex chromosomes shown last)


Karyotype Notations

  • It has to be written in format of:

# of chromosomes, gender, and location of the abnormality if any

46, XY Normal Karyotype

Nondisjunction

  • This is caused when the chromosomes do not separate properly during meiosis, forming a monosomy or trisomy.

    • When a sex cell with an extra or one less chromosome gets fertilized, the zygote will have an extra or one less chromosome.

Trisomy VS Monosomy

  • When there is an extra chromosome in a pair = trisomy

Examples of trisomy disorders:

  • Down syndrome

  • Patau syndrome

  • Klinefelter syndrome


  • When there is only one chromosome in a pair = monosomy

Examples of monosomy disorders:

  • Turner syndrome

  • Cri du Chat Syndrome